Puff, a 6-year-old male sea lion, died unexpectedly Thursday at the Seneca Park Zoo as he was being treated for sinusitis while under anesthesia.

The sea lion had undergone months of treatments for sneezing, bloody mucus and nasal discharge.

"We really didn't expect it," said zoo Director Larry Sorel.

Dr. Jeff Wyatt, the zoo's director of Animal Health & Conservation said: "The necropsy confirmed an invasive necrotizing sinusitis." He said more tests would have to be conducted to determine whether there was an underlying bacterial or fungal cause, and that could take six to eight weeks.

The zoo's three other sea lions - a male, Flounder, 21, and two females, Lily and Marina, both 3 - are not in similar danger.

"This unusual infectious sinus condition is localized and poses no threat to the health of the zoo's other sea lions," Wyatt said.

It will be several weeks before tests reveal a cause of death.

"Normally sea lions live 15 to 20 years before we see them begin to die from old-age related issues," Sorel said.

Puff was born on June 11, 2006, at Sea World Orlando. He arrived in Rochester May 18, 2007. He arrived at 121 pounds and last weighed in at 490 pounds.

"As families learned the difference between seals and sea lions, he was ready and willing to be the center of attention to gain the tasty reward of a piece of squid or smelt," said Rachel Baker August, executive director of the Seneca Park Zoo Society. "He was certainly a crowd pleaser and will be missed by all."

Sorel said the zoo does not plan to replace Puff with another male, at least not right now.

That's because the zoo's two female sea lions may or may not be pregnant. There are no pregnancy tests available for sea lions, so zoo keepers won't know either way until after the next birthing season in June.

"If we want to have future reproduction we will have until June of 2013, then we'll decide," Sorel said.